1. Field of the Invention
This invention relates to novel adhesion agents for polyamide composite structures, particularly for polyamide 12-polybutylene terephthalate composite structures.
2. Description of the Prior Art
The subject matter of the invention relates particularly to new adhesion agents and agents that improve the compatibility hereinafter referred to as compatibility agents! on the basis of high-molecular block (co)polyester amides, produced by direct esterification of carboxyl-terminated or hydroxycarboxyl-terminated polyamide precondensates, hydroxyl-terminated or hydroxycarboxyl-terminated polyester precondensates and a further diol component. The block (co)polyester amides have two separate crystalline phases which are formed by the (co)polyamide and (co)polyester (PES) segments. In addition, the invention relates to a process for the production of these block (co)polyester amides and the use of the block (co)polyester amides for the production of fibers, sheets or films, molded articles and particularly as adhesion agents of corresponding polyamide polyester multilayer or composite structures and as compatibility agents of corresponding polymer blends.
EP-A-0287839 describes inter alia composite structures consisting of polyamide mixtures and polyester resins. Thermoplastics are used as adhesion agents, whose chemical composition differs from the adjacent layers of the composite structure. Functionalized polyolefins, functionalized ethylene-vinyl acetate copolymers, ethylene-acrylate copolymers, ionomers, polyalkylene oxide-polyester block polymers, derivatives of carboxymethyl cellulose as well as blends of these polymers with polyolefins are mentioned as suitable adhesion agents. However, the interlaminar or composite strengths achievable with these adhesion agents in the polyamide/polyester system are little and fully lost during heating or in contact with solvents, since the adhesion agents are not sufficiently thermoforming stable and solvent-resistant.
EP 0509211 B1 and EP 0509212 B1 describe thermoplastic composite structures on the basis of polyamides and polyesters. The described adhesion agents are polyamide-polyester blends which were obtained by reactive extrusion. Reactive extrusion using polyamide and polyester is described inter alia in EP-A-0084643 and in "Polymer Engineering and Science, 24, 1300 (1984). It is disadvantageous that only a minor portion of the blending reactants is converted into copolymers, however with totally undefined structure. The blends usually have poor mechanical properties; particularly their high degree of brittleness is marked. As compared to the corresponding initial components, the composite strength of these blends is usually only sufficient for one blending reactant.
EP 042008 B1 discloses polyester amides containing benzenedicarboxylic acids and 1,4-butanediol in the polyester portion and .omega.-aminoundecanoic acid and .omega.-aminododecanoic acid, respectively, in the polyamide portion. Since the polyamide components are used as monomers, a random incorporation of the components results, on the one hand, and a partial degradation of the polyester precondensate results, on the other hand. Because of their structure, such materials are unsuitable to act as adhesion agents.
The block polyester amides described in DE-A-3435053 are made from block polyamide dicarboxylic acids having a mean molar mass of 1000-8000 g/mole and block polyester diols. However, the described mode of operation effects a strong degradation of the polyamide and polyester blocks used. Here, too, the polyamide and polyester portions only have minor polymerization degrees. A phase-mediating effect for correspondingly composed homopolymers does not occur, since none of the adjacent polymer layers is wetted in optimum fashion by the mean surface tension of the random polyester amides, on the one hand, and major chain sections cannot interact without disturbances, on the other hand. The low melting point of random polyester amides rapidly leads to a loss of composite strength in the case of heating. In addition, random polyester amides have tear resistance little as compared to polyamides and polyesters.
DE-A-2129476 describes hot-melt adhesion agents on the basis of a block polyester amide having high thermostability. The block polyester amide consists of a partially crystalline polyester portion and an amorphous polyamide portion. The polyester segments are produced in situ by glycosylation and transamidation, based on high-molecular polyesters. The operating mode as well as the melting points low as compared to the homopolyester suggest short block lengths and/or intense amide-ester exchange reactions. The polyester amides used as hot-melt adhesion agents have a relatively low molar mass. Similar products are described in U.S. Pat. No. 4,548,996 and GB-A-1340214.
U.S. Pat. No. 3,849,514 describes block polyester amides having improved segment stability. Before further reacted with polyester diols, the precondensates synthesized from diamines and dicarboxylic acids have to be provided with ester or hydroxyl ester terminal groups. A variant consists in the synthesis of the ester-masked polyamide precondensates by aminolysis of the diesters of dicarboxylic acids, the phenolate being used preferably. When the reaction proceeds, phenol has to be distilled off. The polyamide portion is restricted to polyamides of the AABB type. Lactams and .omega.-aminocarboxylic acids are not listed as monomers.
Most of the polymers are incompatible with one another. Therefore, suitable adhesion agents and compatibility agents, respectively, have to be used for the production of efficient composite structures and polymer mixtures. Optimum interaction between polymer and a suitable adhesion agent can only be assumed if identical structural units of sufficient size can interact with one another. Therefore, the above-mentioned prior art adhesion agents which have a structure and chemical composition differing from polyamide and polyester are suited for polyamide-polyester composite structures only to a point.
Most of the above-described polyester amides are lacking the defined structure, particularly the polyamide and polyester segments have excessively small polymerization degrees because of the employed monomers or the production process, so that the interaction with respect to polyamide and polyester remains on a low level. The achieved molar masses and thus the melt viscosities are also often too low for these materials to be processed by extrusion and to include sufficient mechanical properties. An adhesion agent effect for corresponding polyamide-polyester composite structures is not described. Because of the rather random structure of these products this cannot be expected either. Moderate mechanical properties and the low melting temperature of these products further restrict the possible uses. In addition, the random polyester amides dissolve in many current solvents, so that the composite structure is also dissolved upon the influence thereof.